The objective of the research is to study the occurrence of twins in the offspring of twins themselves, in the offspring of sibs of twins and in the grandchildren of the twins and sibs. By computing twinning rates for these various groups we propose to investigate the method of inheritance of dizygotic twinning. We also propose to study the apparent inability of males to transmit the twinning factor to their daughters. Our preliminary results have pointed to this finding which is far unexplained in terms of nuclear inheritance.